1. Field of the Invention
The present invention relates to a substrate defect inspection method, a computer readable storage medium storing a program for causing a computer to execute the method, and a defect inspection apparatus.
2. Description of the Related Art
In a photolithography process in a manufacturing process of a semiconductor device, for example, a resist coating treatment for forming a resist film on a front surface of a substrate such as a wafer, exposure processing for irradiating a pattern on the front surface of the substrate for exposure, a developing treatment for developing the substrate after the exposure and so on are performed. The substrate for which a series of predetermined photolithography process steps has been completed is subjected to a so-called macro defect inspection by an inspection unit, such as whether or not a predetermined resist film is formed on the front surface of the substrate, or whether or not appropriate exposure processing is performed.
The above-described macro defect inspection is performed by moving a mounting table mounting a substrate thereon in X- and Y-directions on the same plane and causing an image pickup means such as a CCD camera fixedly provided above the substrate to scan the top of the substrate so as to pick up an image of the front surface of the substrate (Japanese Patent Application Laid-open No. 2001-168010). The image obtained by the image pickup is subjected to image processing to detect the presence or absence of a defect. In more detail, there occurs a difference in luminance or in brightness and darkness in picked-up images between a normal substrate and a substrate having a macro defect such as defocus, uneven application or the like, the difference appearing as a difference in pixel value on image data. In the prior art, the difference is utilized to obtain a difference image of an absolute value by subtracting the image of a normal substrate from the image of the substrate being an inspection object, and the difference image is simply binarized into numerical values, so that whether the substrate is normal or abnormal, that is, whether there is a defect, is determined depending on whether the numerical value exceeds a previously set threshold value (Japanese Patent Application Laid-open No. H6-18436 and Japanese Patent Application Laid-open No. 2004-85503).
In the above-described method, however, if the difference image is binarized, for example, it is difficult to set the threshold value as a reference to perform determination whether the substrate is normal or abnormal because the absolute values of the binarized values are small, and therefore erroneous determination can be made. Besides, it is necessary to accurately mount the substrate being the inspection object at a predetermined image pickup position in all of the X-direction, Y-direction and θ-direction when picking up an image of the substrate. This additionally requires an alignment work using, for example, a notch aligner or the like for the accurate mounting, thus taking extra inspection time.